Correlation does not imply causation

1a. Provide an example of two variables that are correlated, but where there is no causal connection between them.

1b. Provide an example of two variables that are correlated, and where one variable is a cause of the other.

1c. What exactly does "correlation does not imply causation" mean? Does it mean that if two variables are correlated, they can never be related causally?